HIV associated cardiac pathology is being recognized increasingly as patients with chronic HIV infection who survive to live productive lives. HIV associated cardiomyopathy is among the most common cardiac specific manifestation of chronic HIV infection and was observed in between 6-12% of patients that succumb to AIDS. However, cardiovascular involvement has emerged as more than a pathologic curiosity, but rather as a significant cause of morbidity as individuals live longer, more productive lives with HIV. Increased use of HAART therapy has served to unmask HIV associated predispositions to cardiac involvement. Despite the increased recognition, the risks factors for, the pathogenesis of, and the specific treatments required in HIV associated cardiac disease remain unknown. The nonhuman primate model of SIV infection in rhesus macaques affords an unparalleled opportunity to study these critical features. Prior work from our laboratory has characterized the time course, the role of CIM counts, and the pleomoprhic cardiac manifestations in simian AIDS. The work has demonstrated the need to consider both viral and host factors in identifying those at increased risk and to create a consistent, reproducible model of cardiac involvement for further investigation. We have determined that macrophage-tropic strains of SIV are most commonly associated with lymphocytic myocarditis. SIV is localized to the myocardium in approximately one third of cases of cardiac involvement, and when present, always co-localizes to cells of the macrophage lineage, either tissue macrophages or cardiac dendritic cells. TNFalpha, produced by activated macrophages, mediates both up-regulation of NOS2 in cardiac myocytes and the expression of Fas (CD95) receptors leading to cardiac myocyte apoptosis. As such, we have shown that cytokines play a central mechanistic role in both reversible LV dysfunction (increased NF-kappaB NOS2 expression) and irreversible myocardial injury (Fas-FasL mediated apoptosis). In addition, lymphocytic infiltrates are frequently perivascular and associated with coronary vascular lesions characterized by endothelial activation, smooth muscle proliferation, and thrombotic occlusions, leading to acute ischemic injury. These pathological features are mirrored in the lung where lymphocytic interstitial pneumonia and pulmonary vasculopathy are observed and contribute to increased right ventricular dysfunction. We plan to explore both host and viral factors that lead to SIV transmission into the myocardium (SIV cardiotropism) and SIV mediated injury (cardiovirulence). The identified mechanisms will serve as a prerequisite for exploring specific strategies to prevent cardiac involvement in chronic SIV infection.